BeePre Build Help Needed [resolved]

[markamon]

Greetings Bottleheaders-
I built the Foreplay years ago and it had no issues.
It still sounds sweet.
For the BeePre I have some resistances off for starters and would be very grateful for your help.
Here are the resistances measured with a Fluke Automotive 88V.
I have marked readings that seem to be off with "**"

1-  4.1 ohm
2-  395 K-ohm
3-  0
4-  4.9 ohm/unstable
5-  0
6-  145.3 K-ohm
7-  470 K-ohm
8-  0
9-  0
**10- starts high, greater than 1 M-ohm, continues to fall gradually

11- 145.1 K-ohm
**12- 0
13- 0
14- 0
**15- starts high, greater than 1 M-ohm, continues to fall gradually
16- 4.2 ohm
17- 393 K-ohm
18-  0
19-  5.0 ohm with 300B/unstable without

20-  0
21-  0
22-  greater than 100 K-ohm
23-  0
24-  0
25-  greater than 100 K-ohm
26-  0
27-  0
28-  0
29-  fluctuates

30-  0.6 M-ohm
31-  0.6 M-ohm
32-  0
33-  0
34-  fluctuates
35-  275 K-ohm
36-  260 K-ohm
37-  0
38-  0
39-  0

40-  greater than 100 K-ohm
41-  0
42-  0
43-  greater than 100 K-ohm
44-  0
45-  0
46-  greater than 100 K-ohm
47-  NA
48-  605 ohm
49-  0
50-  NA
51-  604 ohm

**A1-  600 ohm not stable
A2-  400 K-ohm
A3-  7.5 K-ohm
**A4-  4.2 ohm

B1-  4.3 ohm
**B2-  65 K-ohm
B3-  7.5 K-ohm
**B4-  600 ohm not stable

C2,D2-  215 ohm, 215 ohm
C3,D3-  OL
C4,D4-  600 ohm, 600 ohm
C5,D5-  400 ohm, 400 ohm
C7,D7-  145 K-ohm, 145 K-ohm
C9,D9-  145 K-ohm, 145 K-ohm

Hakko 936
Cardas Quad Eutectic solder
Any ideas where the bad joints or mistaken wiring might be?

Thank you for your assistance.

Mark

 

[Paul Birkeland]

Could you post some build photos?  Also what is the date on the PDF of your manual?

 

[markamon]

The manual is the October 22, 2014 revision.
Attempting to post some photos especially of the terminal 12 area.
If you can let me know what views are best I can work on that.
Thank you,
Mark

 

[Paul Birkeland]

**12- 0

Can you double check this one?  This should just have the resistor, cap, and CAT5 connected to it.

**A1-  600 ohm not stable
**A4-  4.2 ohm

A4 looks like one wire may not be well captured by solder.

**B2-  65 K-ohm
**B4-  600 ohm not stable

I wouldn't be so worried about B2, but B4 is concerning.  Perhaps in the photo what I'm seeing is B4 that's not well soldered rather than A4.

 

[markamon]

Paul,

I rechecked 12, still have 0 ohms, removed the blue and blue-white leads, stripped them back to fresh, removed all the old solder, and soldered then in place again with the resistor. I then removed both red lines at B4, verified their continuity, and resoldered at both ends of both lines, including POS OUT.

B2 now reads greater than 100 K-ohm as it should
B4 still 600 ohm and not stable
12 (& 13) still reads ground
However I found no resistance (0.1 ohm)  across the resistor between 12 and 13 ... so it looks like I need a new one of those before going on? (I checked the other side and it reads 470 K-ohm.)

Thank you,
Mark

 

[Paul Birkeland]

It is very unlikely to be the resistor.  You could have an error back by the RCA/XLR sockets that is causing this, like say solder shorting the RCA output jack on that channel.

 

[Paul Birkeland]

For the B4 issue, are you 100% certain you have the socket installed in the correct orientation?  If the fat pins aren't in the back, then you'll end up with some issues. 

 

[markamon]

Yes sir, very nice, strand of solder shorting the Left RCA output jack.
Restored the 12 reading to 470 K-ohm.
The B4 is still unstable.
I am pretty sure about the 300B socket orientation.
I attempted to attach an image showing both of them, if you can verify.
Thank you!
Mark

 

[Paul Birkeland]

With the 300Bs plugged in, A4 and A1 are shorted together by the 300B filament, which will be under 4 ohms with a cold tube.  You are seeing the correct resistance on A4 that is the filament bias resistors going to ground.

Now I'm noticing that you have the same resistance reading on A1 and B4, so this may simply be your meter unable to cope with the big cap that's there, so I think you can ignore this for now.  If there is an actual issue, it will become very apparent with the voltage checks.

 

[markamon]

Got it.
That meter is designed for automotive so... I'm sure you're right.
Will proceed.
Thank you so much Paul!
Mark

 

[markamon]

Here are the voltages just now.
The only issues I can see are on the Left side EL84 pins.
D3 is low, and D7 and D9 are high.
I also swapped the EL84 tubes for comparison.
Something still seems wrong on the Left.
Again I marked the off readings with "**".

1-  4.87V
2-  92.6V
3-  0
4-  9.86V
5-  0
6-  145V
7-  0
8-  0
9-  0
10-  187V

11-  145V
12-  0
13-  0
14-  0
15-  186V
16-  4.99V
17-  92.0V
18-  0
19-  9.91V

20-  0
21-  0
22-  214V
23-  0
24-  0
25-  214V
26-  0
27-  0
28-  0
29-  6.91V

30-  6.91V
31-  13.9V
32-  0
33-  0
34-  13.9V
35-  6.90V
36-  6.90V
37-  0
38-  0
39-  0
40-  214V
41-  0
42-  0
43-  214V
44-  0
45-  0
46-  214V
47- 
48-  0
49-  0
50- 
51-  0

A1-
A2-  92.6V
A3-  0
A4-

B1-
B2-  91.9V
B3-  0
B4-

C2,D2-  0,0
**C3,D3-  4.69,3.98V
**C7,D7-  145,164V
**C9,D9-  145,163V

Swapping the EL84's yields:

C2,D2-  0,0 
**C3,D3-  4.15,1.95V
**C7,D7-  145,160V
**C9,D9-  145,159V

Mark

 

[Paul Birkeland]

Is C2 well soldered?  I would be looking for a flaky solder joint.

 

[markamon]

Thank you Paul,

I have had a chance to look for bad soldering, re-soldered several questionable joints.
I seem to be making things worse, as I started out with only questionable voltages on the B side, now I have issues on both sides.
I discovered or created at least two new problems.

First new problem- the two LEDs on the B-side C4S board closest to the rear of the preamp do not come on now. Before my re-soldering all the LEDs came on.

Second new problem, the four LEDs of the  A-side go dead after about ten minutes, when it gets hot. Very repeatable. Swapping the 300B tubes does not alter this behavior. Turning the power off and letting it cool down restores functionality and voltages  to the "A" side. The A side comes on reliably from a cool start, and the voltages I obtained below are when the LEDs are on.

1-  4.91V
2-  91.7V
3-  0
4-  9.86V
5-  0
6-  145V
7-  0
8-  0
9-  0
10-  187V

**11-  159V (should be 146V)
**12-  91.5V (should be 0V)
13-  0
14-  0
**15-  168V (should be 186V)
16-  4.93V
17-  91.5V
18-  0
19-  9.92V

20-  0
21-  0
22-  213V
23-  0
24-  0
25-  213V
26-  0
27-  0
28-  0
29-  6.80V

30-  6.81V
31-  13.7V
32-  0
33-  0
34-  13.9V
35-  6.89V
36-  6.89V
37-  0
38-  0
39-  0
**40-  205V (should be 213V)
41-  0
42-  0
**43-  205V (should be 213V)
44-  0
45-  0
**46-  205V (should be 213V)
47-
48-  0
49-  0
50-
51-  0

A1- ?
A2-  91.2V
A3-  0
A4-  ?

B1-  ?
B2-  91.3V
B3-  0
B4-

C2,D2-  0,0
**C3,D3-  3.93,1.96V
**C7,D7-  145,158V
**C9,D9-  145,187V

Mark

 

[Paul Birkeland]

Are you 100% sure you have 90V on 12?  Are you sure it's not 90mV or 90uV?

 

[markamon]

I am sure it was 91.5V earlier as it was surprising and I rechecked it several times.
When I powered up again just now to recheck it to try to answer the 100% sure aspect of your question, I found all four of the LEDs on the B side to be dark, instead of only two, and the voltage now at terminal 12 is 0.20V, decaying slowly down.

 

[Paul Birkeland]

How's the resistance at 12?  That issue will happen if the 475K resistor is damaged or disconnected. 

 

[Paul Birkeland]

I'd also want to see the bottoms of the C4S board and low voltage regulator board on the offending side.  In your initial photos, there were definitely some solder joint issues on those boards, but you mentioned you reflowed the joints.

 

[markamon]

The resistance at terminal 12 is 473 k-ohm.
I have attached images of the bottoms of the B-side boards, the side with 4 dark LEDs.

 

[Paul Birkeland]

Can you tell me about the soldering products you're using.  Solder? Flux? Iron? Other stuff?

 

[grufti]

There is definitely one wire in the center of B that is not soldered at all. It's not difficult to see.